If it's too good to be true, it usually is. Nobody will send you money just to turn around and have you send it back if you have won a prize.
The IRS/Government agency's will not call you and ask you to reply by send money or the local Sheriff's Office will be out to arrest you.
If your grand kids are in jail and ask you to wire money to a non-corrections facility but they do not want you to contact their parents to confirm this, this is a good indication it is a scam. Always verify who is calling and confirm with their parents their whereabouts before even thinking about sending money.
There are too many scams going on to mention them all but if your ever in doubt, call or stop at the Sheriff's Office to talk with somebody before considering sending money and giving any personal information out over the phone or the Internet.